1. Field of the Invention
This invention relates to an ophthalmic apparatus capable of detecting the state of alignment of an eye to be examined.
2. Description of Related Art
When an ophthalmic apparatus is to be used, for example, when the fundus of an eye to be examined is to be photographed by an eye fundus camera or when the refractive power of an eye is to be measured by an eye refractometer, it is important in achieving an exact and highly accurate examination or measurement to properly carry out the alignment adjustment for aligning the optic axis of the eye examining instrument with the visual axis of the eye to be examined, and the operation of making the operating distance between the eye to be examined and the eye examining instrument coincident with an optimum value.
Numerous means for carrying out the alignment adjustment and the operating distance adjustment have already been proposed. Many of those propositions utilize the fact that the surface of the cornea of the eye to be examined has a function corresponding to a convex mirror. In the case of this method, the eye examining instrument can be adjusted so that the optic axis thereof passes through the vertex of the cornea. It is not always ensured that the optic axis will pass through the center of the pupil because there is an individual difference in the positional relation between the cornea and the pupil.
Accordingly, depending on the eye to be examined, an error in examination or measurment occurs and reduces the accuracy of examination or measurement. Also, where the convex mirror function of the surface of the cornea is utilized, if the reflected light from the cornea varies greatly in conformity with the state of alignment due to the radius of curvature of the cornea being small and the tolerance within which the reflected light from the cornea can be detected for the detection of the state of alignment is so small that the positional relation between the eye to be examined and the ophthalmic apparatus is generally incoincident, it has been impossible to detect the positional information of the eye to be examined.
Further, when the eye to be examined is to be photographed or measured by an eye fundus camera or an eye refractometer, photographing, photographing or measurement cannot be accomplished unless the diameter of the pupil of the eye to be examined is open over a predetermined value. Heretofore, the examiner has judged by seeing the image in the viewfinder or on the TV monitor. But this leads to a disadvantage of requiring an experienced examiner. Also, where the diameter of the pupil of the eye to be examined is somewhat greater than a predetermined value, photographing or measurement can be accomplished, but the adjustment of the alignment with the eye to be examined must be strict and in this respect requires attentiveness by the examiner.